CN102298468B - Object image capturing device and method for capturing object image of pointer - Google Patents

Abstract

The invention relates to an object image capturing device and a method for capturing an object image of an indicator. The device is suitable for an optical touch system and used for capturing an object image of an indicator when the indicator interacts with a touch surface of the optical touch system. The device comprises an image sensing device and a processing circuit. The image sensing device is used for sensing an image of the touch surface. When the indicator is close to the touch surface, the processing circuit compares information in a sensing image with a threshold value to find out a comparison range, and generates another threshold value according to the image information in the comparison range to compare with the image information in the comparison range so as to capture an object image of the indicator.

Description

Object image capturing device and method for capturing object image of pointer

technical field

The present invention relates to an optical touch technology, and in particular to an object image capture device and a method for capturing an object image of a pointer.

Background technique

Resistive touch screen can be said to be the most widely used touch technology at present. Its driving principle is to use the method of voltage drop to calculate the coordinates, that is, to apply a voltage to each of the multiple X-axis and Y-axis lines to drive . When the resistive touch screen is touched, a voltage drop will occur due to the conduction of the circuit, and the controller will calculate the proportion of the voltage drop and then further calculate the coordinate axis.

FIG. 1 is a perspective view of a conventional optical touch system. Please refer to FIG. 1 , the optical touch system 100 includes an object image capture device 101 , a panel 104 , and reflective elements 112 - 116 . Wherein, the object image capturing device 101 further includes image sensing devices 106 and 108 , and a processing circuit 110 . Both the image sensing devices 106 and 108 are used for sensing the image of the touch surface 118 on the aforementioned panel 104 . The processing circuit 110 is electrically coupled to the image sensing devices 106 and 108 to receive images sensed by the two image sensing devices. In this example, the shape of the touch surface 118 is quadrangular, preferably rectangular. As for the reflective elements mentioned above, they are all used to reflect light to the touch surface 118 , but none of them will form a mirror image of the touch surface 118 . When the pointer 102 is close to the touch surface 118 , the processing circuit 110 obtains the position of the pointer 102 according to the images sensed by the two image sensing devices.

FIG. 2 is an explanatory diagram of a single-point touch performed by the optical touch system 100 . In FIG. 2, the same reference numerals as those in FIG. 1 denote the same components. As shown in FIG. 2 , the image sensing device 106 can sense the pointer 102 along the sensing route 202 , and the image sensing device 108 can sense the pointer 102 along the sensing route 204 . Therefore, as long as the processing circuit 110 can obtain the linear equation of the sensing route 202 according to the image sensed by the image sensing device 106, and obtain the linear equation of the sensing route 204 according to the image sensed by the image sensing device 108, Then the processing circuit 110 can calculate the intersection of the sensing routes 202 and 204 , so as to further calculate the coordinates of the pointer 102 according to the intersection.

Before calculating the coordinates of the pointer 102, the processing circuit 110 must first find out the imaging range of the pointer 102 in the image sensing window of the image sensing device 106 from the image sensed by the image sensing device 106 (details will be described later). ), that is, the processing circuit 110 must first capture the object image of the indicator 102 from the image sensed by the image sensing device 106, so as to further obtain the linear equation of the sensing route 202, and at the same time, the processing circuit 110 must also obtain the image from the image The image sensed by the sensing device 108 is used to find the imaging range of the indicator 102 in the image sensing window of the image sensing device 108 (described in detail later), that is, the processing circuit 110 must first obtain the image sensed by the image sensing device 108. The detected image is used to capture the object image of the pointer 102 so as to further obtain the linear equation of the sensing route 204 . This will be further explained below.

Taking the operation between the processing circuit 110 and the image sensing device 106 as an example, before the pointer 102 approaches the touch surface 118, the processing circuit 110 will first sense the touch surface 118 through the image sensing device 106 to obtain a different An image of the object image containing the pointer 102 is used as a background image. Then, the processing circuit 110 will obtain the luminance values of the N brightest pixels in each row of pixels of the background image, and calculate the average brightness or total brightness value of the selected N brightest pixels in each row of pixels, and then form a Brightness distribution map, where N is a natural number. The luminance distribution graph is presented as a curve, because the background luminance is usually not in a uniform relationship. FIG. 3 is an example of a brightness distribution diagram obtained from a background image, and any point in the curve shown in this figure represents the brightness value of a row pixel of the background image.

Then, when the pointer 102 is close to the touch surface 118 , the processing circuit 110 can obtain an image of the object image containing the pointer 102 through the image sensing device 106 . FIG. 4 is a schematic diagram of an image sensed by an image sensing device. In FIG. 4 , a mark 400 represents an image sensing window of the image sensing device 106 . The white area indicated by the mark 402 is the light reflected by the reflective elements 114 and 116 to form a bright zone with higher brightness on the image, and the bright zone 402 is the main sensing zone. As for the mark 404, it is the dark lines caused by the indicator 102, which is the object image.

After acquiring the image of the object including the pointer 102 , the processing circuit 110 regards the image as a sensing image, and obtains the brightness distribution map of the sensing image using the same method as obtaining the aforementioned brightness distribution map. FIG. 5 is another luminance distribution diagram described above. In FIG. 5 , the curve indicated by the mark 502 is the luminance distribution diagram obtained from the sensing image, and any point in this curve represents the luminance value of a row pixel of the sensing image. The range indicated by the mark W ₁ is the low brightness range caused by the indicator 102 shielding the light. The curve indicated by the mark 504 is a threshold value, and the threshold value 504 is obtained by the processing circuit 110 from the luminance distribution map (as shown in FIG. 3 ) obtained from the above-mentioned background image according to a preset percentage.

Please continue to refer to FIG. 5 , after obtaining the brightness distribution diagram 502, the processing circuit 110 compares the brightness distribution diagram 502 with the threshold value 504, so as to identify the part of the brightness distribution diagram 502 whose brightness value is lower than the threshold value 504 (indicated by W ₁ ) corresponds to the distribution range of the row of pixels, which is regarded as the imaging range of the pointer 102 in the image sensing window 400 of the image sensing device 106 . In other words, the processing circuit 110 captures the image information of the imaging range _W1 as the object image of the pointer 102 . In this way, the processing circuit 110 can further obtain the linear equation of the sensing route 202 according to the imaging range, for example, calculate the center of gravity of the imaging range to further obtain the linear equation of the sensing route 202 . Similarly, the operation between the processing circuit 110 and the image sensing device 108 can also be performed according to the operation between the processing circuit 110 and the image sensing device 106 to further obtain the linear equation of the sensing route 204 .

However, the optical touch system 100 often has problems when performing multi-touch. Taking the operation between the processing circuit 110 and the image sensing device 106 as an example, when two pointers 102 touch the touch surface 118, and the two pointers 102 are very close to each other, then the processing circuit 110 A luminance distribution map is obtained from the sensing image. FIG. 6 is a drawing of the luminance distribution diagram. In FIG. 6 , the curve indicated by the mark 602 is the luminance distribution diagram obtained from the sensing image, and any point in this curve represents the luminance value of a row pixel of the sensing image. The range indicated by the mark W2 is the low brightness range caused by the two indicators 102 blocking the light. The curve indicated by the mark 504 is a threshold value, and the threshold value 504 is obtained by the processing circuit 110 according to a preset percentage from a luminance distribution map obtained from a background image.

As can be seen from FIG. 6 , when the threshold value 504 is set too high, the processing circuit 110 will regard the two pointers 102 as the same pointer. Therefore, the processing circuit 110 cannot further calculate the coordinates of the two pointers 102 .

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide an object image capture device, which can accurately capture the respective object images of a plurality of pointers.

Another object of the present invention is to provide a method for capturing object images of pointers, which can accurately capture object images of multiple pointers.

The present invention provides an object image capture device, which is suitable for an optical touch system, and is used for capturing an object image of a pointer when the pointer interacts with a touch surface of the optical touch system. The object image capturing device includes an image sensing device and a processing circuit. Wherein, the image sensing device is used for sensing the image of the touch surface. The processing circuit is coupled to the image sensing device. When the pointer is close to the touch surface, the processing circuit obtains a sensing image through the first image sensing device, and compares information in the sensing image with a first threshold value to find a comparison range . In addition, the processing circuit also generates a second threshold value according to the image information in the comparison range, so as to compare the image information in the comparison range with the second threshold value for capturing the object image of the indicator.

In a preferred embodiment of the object image capture device of the present invention, wherein the processing circuit compares all or part of the information in the sensing image with a first threshold value to find a comparison range, All or part of the information in the sensing image includes the processing circuit obtaining the brightness values of the N brightest pixels in each row of pixels in the sensing image, and calculating the average brightness of the selected N brightest pixels in each row of pixels value or the total brightness value, and then form the first brightness distribution map, where N is a natural number.

In a preferred embodiment of the object image capture device of the present invention, the comparison range mentioned above is the range covered by all row information in the first brightness distribution graph whose brightness value is lower than the first threshold value.

In a preferred embodiment of the object image capture device of the present invention, the first threshold value is obtained by the processing circuit from a second brightness distribution map obtained from a background image according to a first preset percentage. The background image is a pre-acquired image of the object without the pointer by the processing circuit sensing the touch surface through the image sensing device before the pointer approaches the touch surface. The second brightness distribution diagram is obtained by the processing circuit by calculating the average brightness or the total brightness of the N brightest pixels selected in each row of pixels of the background image.

In a preferred embodiment of the object image capture device of the present invention, the above-mentioned processing circuit obtains the second threshold value from the second brightness distribution map according to a second preset percentage.

In a preferred embodiment of the object image capture device of the present invention, the processing circuit obtains a minimum point from the curve segment corresponding to the comparison range of the first brightness distribution graph, and uses the brightness of the minimum point The second threshold value is obtained by adding predetermined brightness to the reference value.

In a preferred embodiment of the object image capturing device of the present invention, capturing the object image of the pointer includes capturing image information in the comparison range that is smaller than the second threshold value as the object image.

The present invention also provides a method for capturing an object image of a pointer, which is suitable for an optical touch system. The optical touch system includes a touch surface and an image sensing device. Wherein, the image sensing device is used for sensing the image of the touch surface. The method includes the following steps: when an indicator is close to the touch surface, using an image sensing device to obtain a sensing image, and comparing information in the sensing image with a first threshold value to find a Comparing the range; generating a second threshold value according to the image information in the comparison range; and comparing the image information in the comparison range with the second threshold value to extract the object image of the indicator.

In a preferred embodiment of the method of the present invention, all or part of the information in the sensing image is compared with a first threshold value to find a comparison range, wherein all or part of the information Including the first brightness distribution formed by obtaining the brightness values of the N brightest pixels in each row of pixels of the sensed image, and calculating the brightness average or total brightness value of the selected N brightest pixels in each row of pixels graph, where N is a natural number.

In a preferred embodiment of the method of the present invention, the comparison range mentioned above is the range covered by all row information in the first brightness distribution graph whose brightness value is lower than the first threshold value.

In a preferred embodiment of the method of the present invention, the above-mentioned first threshold value is obtained according to a first preset percentage from a second luminance distribution map obtained from a background image. The background image senses the touch surface through the image sensing device before the pointer is close to the touch surface, so an image of the object image without the pointer is obtained in advance. The second brightness distribution map is obtained by calculating the brightness average value or total brightness value of the N brightest pixels selected in each row of pixels of the background image.

In a preferred embodiment of the method of the present invention, the above-mentioned second threshold value is obtained through the second brightness distribution map according to a second preset percentage.

In a preferred embodiment of the method of the present invention, a lowest point is obtained from the curve segment corresponding to the above-mentioned comparison range of the first brightness distribution graph, and the brightness value of the lowest point is used as a reference to increase The predetermined brightness is used to obtain the second threshold value.

In a preferred embodiment of the method of the present invention, capturing the object image of the indicator includes capturing image information in the comparison range that is smaller than the second threshold value as the object image.

The optical touch system of the present invention uses two different threshold values to find object images (ie, actual imaging ranges) of multiple pointers. In the actual operation mode, the processing circuit first uses the first threshold value to find out the approximate imaging ranges of the multiple pointers in the image sensing window of the image sensing device, and the approximate imaging ranges need to be further compared. Compare range. Then, the processing circuit generates a second threshold value according to the image information in the comparison range, so as to compare the image information in the comparison range with the second threshold value, and then extract the object images of these indicators, that is, find out The actual imaging range of these indicators. In this way, the coordinates of the above indicators can be further calculated according to the actual imaging range.

Therefore, as long as the size of the second threshold value is properly designed, the processing circuit can accurately find the object images of these indicators, and then calculate the actual coordinates of these indicators.

The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable , the following specific examples, and with the accompanying drawings, are described in detail as follows.

Description of drawings

FIG. 1 is a perspective view of a conventional optical touch system.

FIG. 2 is an explanatory view of a conventional optical touch system performing single-point touch.

FIG. 3 is an example of a brightness distribution map obtained from a background image.

FIG. 4 is a schematic diagram of an image sensed by an image sensing device.

FIG. 5 is another brightness distribution diagram.

FIG. 6 is another brightness distribution diagram.

FIG. 7 is another brightness distribution diagram.

FIG. 8 is an image sensing device suitable for use in the optical touch system of the present invention.

FIG. 9 is a flowchart of a method for capturing an object image of a pointer according to an embodiment of the present invention.

Detailed ways

The hardware architecture adopted by the optical touch system of the present invention is the same as the hardware architecture adopted by the optical touch system shown in FIG. Do it another way. Therefore, the operation of the optical touch system of the present invention will be described below using the hardware architecture shown in FIG. 1 .

Please refer to Figure 1. As shown in FIG. 1 , the touch surface 118 has four sides connected in sequence (not shown), and the image sensing devices 106 and 108 are disposed on two different corners of the touch surface 118 , and both are located on the touch surface 118 on the same side. In this way, the image sensing devices 106 and 108 can sense images of the touch surface 118 from two different angles.

Next, the multi-touch method of the optical touch system of the present invention will be described. Taking the operation between the processing circuit 110 and the image sensing device 106 as an example, the processing circuit 110 will first sense the touch surface 118 through the image sensing device 106 before any indicator 102 approaches the touch surface 118, so that An image of the object image without the pointer 102 is obtained, and this image is used as a background image. Then, the processing circuit 110 will obtain the luminance values of the N brightest pixels in each row of pixels of the background image, and calculate the average brightness or total brightness value of the selected N brightest pixels in each row of pixels, and then form a Brightness distribution map, where N is a natural number.

Then, when there are two pointers 102 adjacent to the touch surface 118 and the two pointers 102 are quite close to each other, the processing circuit 110 can obtain the object containing the two pointers 102 through the image sensing device 106 Image of image. After acquiring the image of the object image including the two pointers 102, the processing circuit 110 regards the image as a sensing image. Certainly, the sensing image is a sensing image including infrared luminance information. Then, the processing circuit 110 compares all or part of the information in the sensing image with the first threshold value to find out the approximate imaging ranges in the image sensing windows of the image sensing device 106 of the two pointers 102 , and this approximate imaging range is the comparison range that needs to be further compared (details will be described later). In this example, all or part of the information is obtained by the processing circuit 110 by obtaining the luminance values of the N brightest pixels in each row of pixels of the above-mentioned sensed image, and using the same method as obtaining the above-mentioned luminance distribution diagram. A luminance distribution map. The threshold value is obtained by the processing circuit 110 according to a preset percentage from the luminance distribution map obtained from the background image. FIG. 7 is another luminance distribution diagram described above.

In FIG. 7 , the curve indicated by the mark 602 is the luminance distribution diagram obtained from the sensing image, and any point in this curve represents the luminance value of a row pixel of the sensing image. The range indicated by the mark W ₂ is the low brightness range caused by the two indicators 102 blocking the light. The curve indicated by mark 504 is the first threshold. The function of the dotted line indicated by the mark 702 will be described in detail later. It can be seen from FIG. 7 that the low brightness range indicated by W ₂ is the approximate imaging range of the two indicators 102 in the image sensing window of the image sensing device 106 , that is, the comparison range that needs to be further compared. The comparison range is the range covered by all row information in the brightness distribution map of the sensed image whose brightness value is lower than the first threshold value. In other words, the processing circuit 110 compares the luminance distribution diagram 602 with the first threshold value 504, and compares the part of the luminance distribution diagram 602 whose luminance value is lower than the first threshold value 504 (in the range indicated by the mark _W2 ) ) is regarded as the first imaging range of the two pointers 102 in the image sensing window 400 of the image sensing device 106 . The first imaging range is the approximate imaging range of the two pointers 102 .

Please continue to refer to FIG. 7 , after obtaining the aforementioned comparison range, the processing circuit 110 will generate a second threshold value according to the image information in the comparison range, so as to compare the image information in the comparison range with the second threshold value, Furthermore, the actual imaging ranges of these pointers 110 are found. The method of generating the second threshold will be further described below.

In this example, the processing circuit 110 obtains a minimum point from the curve segment (ie, the curve segment within the range W ₂ ) corresponding to the comparison range (ie, the first imaging range) in the brightness distribution diagram 602 . Since point A and point B in this example are both the lowest points, the processing circuit 110 will randomly select one of these two points. Then, the processing circuit 110 sets a second threshold value between the first threshold value 504 and the brightness corresponding to the lowest point (point A or point B). In this example, the processing circuit 110 adds a predetermined brightness based on the total brightness value of the row of pixels corresponding to the lowest point to obtain the second threshold value. The second threshold value is as shown in FIG. 7 702 shown.

After obtaining the above-mentioned second threshold value 702 , the processing circuit 110 compares the curve segment corresponding to the comparison range of the brightness distribution graph 602 with the second threshold value 702 to capture object images of the two pointers. In this example, the processing circuit 110 regards the distribution range of the row pixels corresponding to the portion of the curve segment where the total brightness value is lower than the second threshold value 702 as the distance between the above-mentioned two pointers 102 in the image sensing device 106 The second imaging range in the image sensing window 400 . The second imaging range is the actual imaging range of the two pointers 102 . In other words, the processing circuit 110 can obtain two curve segments lower than the second threshold value 702 in the luminance distribution map 602 according to the second threshold value 702 , and then calculate the distribution of the row pixels corresponding to the two curve segments. The range is regarded as the actual imaging range of the two pointers 102 in the image sensing window 400 of the image sensing device 106 . Briefly speaking, image information smaller than the second threshold value 702 in the comparison range is captured as the object images of the two indicators. In this way, the processing circuit 110 can further obtain the linear equations of the corresponding two sensing routes according to the actual imaging ranges of the two pointers 102 .

Similarly, the operations between the processing circuit 110 and the image sensing device 108 can also be performed according to the operations between the processing circuit 110 and the image sensing device 106 to further obtain the linear equations of the other two sensing routes. Then, the processing circuit 110 can further obtain the coordinates of the two pointers 102 according to the four linear equations. As can be seen from the above description, even if the above-mentioned two pointers 102 are quite close to each other, the optical touch system of the present invention can still accurately find the object images of the two pointers 102 (that is, the actual imaging range), and then calculate The actual coordinates of the two pointers 102 . Therefore, the optical touch system of the present invention can more accurately perform multi-touch coordinate positioning.

Although in this example, the processing circuit 110 obtains the above-mentioned second threshold value 702 (which is a straight line) by adding a predetermined brightness based on the total brightness value of the row of pixels corresponding to point A or point B, the processing circuit 110 may also be to obtain another threshold value (which is a curve) from the brightness distribution map obtained from the background image according to another preset percentage, so as to replace the brightness threshold value 702 . Of course, another threshold value used to replace the threshold value 702 will be located between the point A (or point B) and the first threshold value 504 . In addition, the processing circuit 110 may also sense the lowest brightness value of the brightness distribution map of the image in the comparison range as the second threshold value. In addition, after the processing circuit 110 obtains a brightness distribution diagram by calculating the brightness value of each row of pixels of the background image, the brightness distribution diagram can be recorded first, so that such operations do not need to be repeated again and again. In addition, the processing circuit 110 can also obtain the background image through one of the image sensing devices, and then obtain the sensing image through another image sensing device.

In addition, with the help of the above teachings, those skilled in the art should know that even if the object image capture device 101 only includes an image sensing device and a processing circuit, the object image capture device 101 can still perform the above-mentioned object acquisition of the pointer. The image operation can accurately capture the respective object images of multiple pointers. It is worth mentioning that each reflective element in this example can be made of retro-reflective material to achieve a better effect. In addition, each reflective element in this example can be replaced by a light emitting element, as long as each light emitting element emits light toward the touch surface 118 .

FIG. 8 illustrates an image sensing device suitable for use in the optical touch system of the present invention. Referring to FIG. 8 , the image sensing device 800 includes an infrared (infra-red, IR) illuminating device 802 , an infrared filter device 804 that only allows infrared rays to pass through, and a photosensor (photosensor) 806 . The light sensor 806 obtains the image of the touch surface 118 through the infrared filter device 804 and is coupled to the processing circuit 110 . In addition, the infrared illuminating device 802 can be realized by using an infrared light-emitting diode (IR LED), and the infrared filtering device 804 can be realized by using an infrared filter (IR-pass filter).

With the help of the above teachings, a method for capturing the object image of the pointer can also be summarized, as shown in FIG. 9 . FIG. 9 is a flowchart of a method for capturing an object image of a pointer according to an embodiment of the present invention, which is applicable to an optical touch system. The optical touch system includes a touch surface and an image sensing device. Wherein, the image sensing device is used for sensing the image of the touch surface. The method includes the following steps: when an indicator is close to the touch surface, use the image sensing device to obtain a sensing image, and compare all or part of the information in the sensing image with the first threshold value to find out Create a comparison range (as shown in step S902); generate a second threshold value according to the image information in the comparison range (as shown in step S904); and compare the image information in the comparison range with the second threshold value , for capturing the object image of the pointer (as shown in step S906).

To sum up, the optical touch system of the present invention uses two different threshold values to find object images (ie, actual imaging ranges) of multiple pointers. In the actual operation mode, the processing circuit first uses the first threshold value to find out the approximate imaging ranges of the multiple pointers in the image sensing window of the image sensing device, and the approximate imaging ranges need to be further compared. Compare range. Then, the processing circuit generates a second threshold value according to the image information in the comparison range, so as to compare the image information in the comparison range with the second threshold value, and then extract the object images of these indicators, that is, find out The actual imaging range of these indicators. In this way, the coordinates of the above indicators can be further calculated according to the actual imaging range.

Therefore, as long as the size of the second threshold value is properly designed, the processing circuit can accurately find the object images of these indicators, and then calculate the actual coordinates of these indicators.

The above description is only an embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with the embodiment, it is not intended to limit the present invention. Without departing from the scope of the technical solution of the present invention, when the technical content disclosed above can be used to make some changes or be modified into equivalent embodiments with equivalent changes, but if it does not deviate from the technical solution of the present invention, the technical essence of the present invention can be used for the above Any simple modifications, equivalent changes and modifications made in the embodiments still fall within the scope of the technical solution of the present invention.

Claims (18)

1. an object image capture device, for optical touch control system, in order to capture the object image of this indicant in the time that touch-control surface of an indicant and this optical touch control system is interactive, is characterized in that comprising:

An Image sensor apparatus in order to this touch-control surface image of sensing; And

A treatment circuit, couple this Image sensor apparatus, in order in the time that this indicant is close to this touch-control surface, this treatment circuit is obtained a sensing image by this Image sensor apparatus, and the information in this sensing image and first threshold value are compared, to find out a comparison scope of the information in this sensing image, and produce second threshold value according to the image information in this comparison scope, the relatively image information in this comparison scope and this second threshold value, the image information that is less than this second threshold value to capture in this comparison scope obtains the object image of this indicant.

2. object image capture device according to claim 1, it is characterized in that: this treatment circuit is in order to compare all or part of information in this sensing image and first threshold value, to find out a comparison scope, wherein all or part of information in this sensing image comprises that this treatment circuit obtains the brightness value of N in every row pixel of this sensing image bright pixel, and calculate average brightness or the brightness total value of the bright pixel of N selected in every row pixel, and then first intensity map forming, wherein N is natural number.

3. object image capture device according to claim 2, is characterized in that: the scope that this comparison scope contains lower than all row information of this first threshold value for brightness value in this first intensity map.

4. object image capture device according to claim 1, it is characterized in that: this first threshold value is obtained according to one first default number percent from obtained second intensity map of background video by this treatment circuit, this background video is that this treatment circuit is before contiguous this touch-control surface of this indicant, first by this this touch-control surface of Image sensor apparatus sensing, thereby the image that does not contain this indicant of obtaining in advance, and this second intensity map to be this treatment circuit obtain by average brightness or the brightness total value of calculating N selected in every row pixel of this background video bright pixel.

5. object image capture device according to claim 4, is characterized in that: this treatment circuit is recently to obtain this second threshold value from this second intensity map according to one second default percentage.

6. object image capture device according to claim 2, it is characterized in that: this treatment circuit is obtained a minimum point from the segment of curve corresponding to this comparison scope of this first intensity map, and obtain this second threshold value taking the brightness value of this minimum point as benchmark increases by a predetermined luminance again.

7. object image capture device according to claim 1, is characterized in that: this object image that obtains this indicant comprises that the image information that is less than this second threshold value in this comparison scope of acquisition is as this object image.

8. object image capture device according to claim 1, it is characterized in that: this object capture device further comprises an infrared illumination device and the infrared ray filtering apparatus that can only allow infrared ray pass through, and this Image sensor apparatus is the image of obtaining this touch-control surface by this infrared ray filtering apparatus.

9. object image capture device according to claim 1, is characterized in that: this second threshold value is at this first threshold value and compare corresponding to this between minimum point of segment of curve of scope.

10. one kind captures the method for the object image of indicant, be applicable to optical touch control system, this optical touch control system includes a touch-control surface and an Image sensor apparatus in order to this touch-control surface image of sensing, it is characterized in that the method comprises the following steps:

In the time of contiguous this touch-control surface of an indicant, utilize this Image sensor apparatus to obtain a sensing image, and the information in this sensing image and first threshold value are compared, to find out a comparison scope of the information in this sensing image;

Produce second threshold value according to the image information in this comparison scope; And

The relatively image information in this comparison scope and this second threshold value, the image information that is less than this second threshold value to capture in this comparison scope obtains the object image of this indicant.

11. methods according to claim 10, it is characterized in that: all or part of information in this sensing image and first threshold value are compared, to find out a comparison scope, wherein, all or part of information in this sensing image comprises the brightness value of N in the every row pixel by obtaining this sensing image bright pixel, and calculate average brightness or the brightness total value of the bright pixel of N selected in every row pixel, and then one first intensity map forming, wherein N is natural number.

12. methods according to claim 11, is characterized in that: the scope that this comparison scope contains lower than all row information of this first threshold value for brightness value in this first intensity map.

13. methods according to claim 10, it is characterized in that: this first threshold value is to obtain according to one first default number percent by obtained second intensity map of background video, this background video is before contiguous this touch-control surface of this indicant, first by this this touch-control surface of Image sensor apparatus sensing, thereby obtain in advance not containing the image of this indicant, and average brightness or brightness total value that this second intensity map is selected in the every row pixel by calculating this background video N bright pixel obtain.

14. methods according to claim 13, is characterized in that: this second threshold value is to obtain according to one second default number percent by this second intensity map.

15. methods according to claim 11, it is characterized in that: from the segment of curve corresponding to this comparison scope of this first intensity map, obtain a minimum point, and obtain this second threshold value taking the brightness value of this minimum point as benchmark increases a predetermined luminance again.

16. methods according to claim 10, is characterized in that: this object image that obtains this indicant comprises that the image information that is less than this second threshold value in this comparison scope of acquisition is as this object image.

17. methods according to claim 10, is characterized in that: this sensing image is the sensing image that comprises infrared ray monochrome information.

18. methods according to claim 10, is characterized in that: this second threshold value is at this first threshold value and compare corresponding to this between minimum point of segment of curve of scope.